1. Field of the Invention
This invention relates to hydrostatic transmissions and more particularly to a control circuit which automatically limits engine braking and which also modulates drive pressure build up as the vehicle is initially placed in motion.
2. Background of the Invention
It is well known to provide a hydrostatic transmission in the power train of vehicles to transmit motive force from the vehicle engine to the drive wheels of the vehicle. The hydrostatic transmission does have several drawbacks and objectionable characteristics however. One of the more objectional characteristics is that upon engagement of the hydrostatic transmission into either forward or reverse, a severe jolt or alternatively an excessively high acceleration rate is experienced. This is most noticeable when the vehicle is being operated by a novice operator.
Also a characteristic of a basic hydrostatic transmission is the severe deceleration normally encountered when a speed reduction is initiated by the vehicle operator. When the operator moves the transmission control lever, be it a foot pedal or a hand operated control rod to a lower speed position, the vehicle is momentarily in a coast situation. The reverse loop of the hydrostatic transmission would suddenly be pressurized and vehicle inertia would be driving back through the transmission. This would result in a deceleration rate which would be uncomfortably high.
A similarly high deceleration rate would be experienced in state of the art hydrostatic transmissions if the vehicle operator suddenly moves the control lever to the reverse position when the vehicle is in a forward traveling direction.
Inventions directed toward the control of hydrostatic transmissions countering the aforesaid situations have been disclosed, however, the present invention teaches previously unattainable benefits.